Ten seconds before the earth rumbled in a UC Berkeley lab early Sunday morning, an alarm started blaring -- and an ominous countdown warned that a temblor centered near Napa was moments away.

"Earthquake! Earthquake!" it cautioned, after a quick series of alarms. "Light shaking expected in three seconds."

The successful alert was the biggest test yet in the Bay Area for a type of earthquake early-warning system that's not yet available to the public in the U.S. but already is providing precious seconds of notice before quakes hit in Mexico and Japan.

The ShakeAlert system -- a collaboration between Cal, Caltech, the University of Washington and the U.S. Geological Survey -- could one day stop elevators, control utilities and alert motorists of an impending natural disaster. But before it is reliable enough to launch throughout the West Coast, the system needs about $80 million in equipment, software and other seismic infrastructure upgrades.

So far, despite Gov. Jerry Brown signing a new state law last fall ordering the creation of an early-warning system, the project has received only about $10 million, mostly from a private foundation, said Thomas Heaton, a geophysics professor at the California Institute of Technology. The USGS's earthquake budget is only a fraction of what it was 30 years ago, he said.

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But Sunday's magnitude-6.0 earthquake could trigger a new sense of urgency. Other countries with early-warning systems, including Japan and Mexico, built them only after devastating quakes, said Richard Allen, director of the UC Berkeley Seismological Laboratory. Japan's system has given residents up to a minute's notice of a quake.

"We want to learn from these other examples and not wait until thousands of Californians are killed before we build an early-warning system," Allen said.

Sunday's quake -- the largest in the Bay Area since the magnitude-6.9 Loma Prieta quake in 1989 -- might unleash more seismic activity after decades of relative calm, scientists say.

Earthquakes can transfer stress from one system to another, creating greater risks in the years ahead, said John Rundle, a physics and geology professor at UC Davis.

"It's a little bit concerning that this activity has started and appears to be resuming a more active trend," Rundle said.

As of Sunday afternoon, the Bay Area's larger and more volatile faults remained quiet, said Brad Aagaard, a geophysicist with the U.S. Geological Survey.

"As time goes on, the chances of a large earthquake happening as a result of this one decrease," Aagaard said of the South Napa quake.

Aagaard said Sunday it could be days before scientists are able to pinpoint the fault where the Napa quake occurred at 3:20 a.m., about 6.6 miles below the earth's surface. It happened near -- and possibly within -- the West Napa fault system, he said, but slightly to the south, in an area that is not well-mapped. On Aug. 5, the USGS recorded a magnitude-3.0 quake within 10 kilometers, he said.

Those near the epicenter of Sunday's quake would not have received much, if any, advance notice of the coming quake from an early-warning system. But it could serve to minimize fires and other hazards by automatically turning off gas lines and notifying motorists, who often don't feel the shaking.

Early-alert systems work by detecting primary waves, or P-waves, which move almost imperceptibly through the earth at almost twice the speed of a quake's destructive S-waves, which shake the ground.

Those farther from the epicenter receive more advance warning. Scientists say adding seismic stations at key points along California's faults and improving existing ones could provide even earlier warnings.

BART adopted the test version of ShakeAlert, but its trains were not running during Sunday's 3:20 a.m. earthquake, and the shaking felt in much of the Bay Area wouldn't have been strong enough to trigger a slowdown, Allen said.

The latest earthquake and ShakeAlert test is sure to receive even more attention next month. By sheer coincidence, UC Berkeley is hosting an international forum Sept. 3-5 on earthquake early warning, expecting 165 people from 13 countries.

On the first day, scientists will discuss how to turn ShakeAlert from a fascinating experiment to a lifesaving system. Before then, experts say, the government needs to make the warning system a priority, providing the tens of millions of dollars to build and operate it.

"If we have an earthquake this afternoon," Allen said he tells lawmakers, "you will fund it next week."